As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries as an energy source for the mobile devices has also sharply increased. Accordingly, much research on secondary batteries satisfying various needs has been carried out.
In terms of the material for batteries, the demand for lithium secondary batteries having high energy density, discharge voltage, and output stability is very high. In terms of the shape of batteries, the demand for prismatic batteries or pouch-shaped batteries, which are thin enough to be applied to products, such as mobile phones, and may be used as batteries for a battery module manufactured by stacking the batteries with high integration is very high.
Although a lithium secondary battery has the above advantages, the lithium secondary battery has a fundamental problem of low safety. For example, if a battery is overcharged, electrolyte decomposition at electrodes of the battery is accelerated with the result that combustible gas is generated from the battery. Also, overcurrent of the battery due to various causes, such as an internal short circuit, increases the temperature of the battery with the result that decomposition of components constituting the battery is caused. The battery may easily catch fire due to such overcharge or overcurrent. According to circumstances, the battery may explode. Also, the increase in temperature of the battery due to causes other than overcurrent may cause the above problems. For this reason, various safety elements to solve the above problems are mounted in the lithium secondary battery.
Specifically, a protection circuit of a secondary battery mainly senses voltage, current, and temperature of the secondary battery to inspect a state of the secondary battery. Generally, the protection circuit senses the temperature of a battery cell and the temperature of a field effect transistor (FET) element and performs a protection function when the sensed temperatures exceed a predetermined temperature.
FIG. 1 is a plan view showing a portion of a conventional switching board 10. Referring to FIG. 1, the switching board 10 includes a pair of switching elements 12 and a temperature detection element (not shown) disposed between the switching elements 12. A thermal glue 15 is applied to the temperature detection element (not shown).
The temperatures of the switching elements 12 are measured through the thermal glue 15. In the above structure, however, measured temperatures may be changed depending upon a heat transfer coefficient of the thermal glue. Also, it may be difficult to accurately measure the temperatures of the switching elements 12 due to a heat dissipation effect of the thermal glue. In addition, manufacturing costs and a defect rate may be increased due to the increase in number of manufacturing processes during manufacture of a battery management unit (BMU).
Therefore, there is a high necessity for a technology that is capable of reducing the manufacturing costs of batteries and, at the same time, accurately measuring the temperatures of the batteries while securing a desired degree of safety.